1. Field of the Invention
The present invention relates generally to a magnetic head and a method for producing the same, and magnetic recording and/or reproducing system.
2. Description of Related Art
It is generally known that the efficiency of a magnetic head is rapidly improved as the magnetic path length of a magnetic circuit decreases. For example, as shown in FIG. 18A, the efficiency is rapidly improved as the magnetic path length decreases to 2 μm (=2000 nm) or less. As shown in FIG. 18B, the magnetic path length means the length of a magnetic circuit passing through a magnetic substance portion 52a, magnetic substance portion 53a, magnetoresistance effect element (e.g., GMR(giant magnetoresistance effect) element), magnetic substance portion 53b and magnetic substance portion 52b of a magnetic head.
The construction of a first example of a conventional magnetic head is shown in FIG. 19. This conventional magnetic head comprises a pair of magnetic substance portions 51a and 51b which are constructed so as to form two different gaps G1 and G2, and a magnetoresistance effect element 56 which is provided in the gap G2. The construction of a second example of a conventional magnetic head is shown in FIG. 20. The magnetic head in this second example comprises a pair of magnetic substance portions 52a and 52b which are arranged so as to be spaced from each other by a gap G1, a pair of magnetic substance portions 53a and 53b which are arranged so as to be spaced from each other by a gap G2 which is greater than the gap G1, and a magnetoresistance effect element 56 which is formed as a bridge between the magnetic substance portions 53a and 53b. In the first and second examples, the gap G1 is formed so as to be more close to a medium facing surface than the gap G2.
The magnetic substance portions 51a and 51b of the magnetic head in the first example are formed by lithography at separate steps, respectively, and the pair of the magnetic substance portions 52a and 52b and the pair of magnetic substance portions 53a and 53b of the magnetic head in the second example are formed by lithography at separate steps, respectively.
Therefore, there is a limit to the formation of a fine magnetic path due to an alignment error and the resolution of a photolithography system. For example, even if an advanced stepper is used, there is an alignment error due to the mechanical alignment precision (50 nm) of the stepper and the deformation of the substrate, so that an error of 400 nm is caused. In order to decrease the producing costs, an inexpensive excimer laser is often used for lithography. When the excimer laser is used, the resolution is about 200 nm. As can be seen from FIG. 21, the alignment error expresses a shift from the center of the gap G1, so that the whole alignment error is 800 nm (=400 nm×2). For that reason, it is not possible to form a magnetic head having a magnetic path length which is equal to or less than a value (2000 nm) obtained by doubling a value (1000 nm) obtained by adding the resolution of 200 nm to the alignment error of 800 nm.
As shown in FIG. 21, in order to form a small magnetic path having a high efficiency, it is required to decrease both of the length G2 of a magnetic gap on the opposite side to a medium facing surface 58 and the height H from the medium facing surface 58 to a magnetoresistance effect element 58. In order to increase the line resolution, it is also required to decrease the length G1 of a magnetic gap on the side of the medium facing surface (about 50 nm).
However, in conventional magnetic head structures and conventional methods for producing the same, these requirements can not be satisfied.
Ironically, as can be seen from FIG. 18A, the efficiency of a magnetic head is rapidly improved when the magnetic path length is about 2000 nm or less which can not be formed in the prior art. Even if a small magnetic path is formed by a conventional magnetic head structure, the efficiency is rapidly lowered in the reproduction of a shorter wavelength signal (0.1 μm or less) required in recent years although the reason for this is not clear, so that it can not be used as a high-density recording head. This is the same during a recording operation, not only during a reproducing operation. In conventional recording heads, the efficiency is greatly lowered in the recording at a shorter wavelength although the reason for this is not clear, so that it is not possible to record on low noise medium for a high density, which exceeds 50 Gbpsi (Giga bit per square inch), using current which can be supplied by a recording IC(Integrated Circuit).
It was found that the lowering of the recording/reproducing efficiency in a shorter wavelength region was remarkable when the length of a magnetic path approaches the order of the thickness (100 nm) of a magnetic domain wall of a magnetically soft substance.
As described above, in all of the conventional head structures, a thin-film is patterned by lithography to form a magnetic circuit. Therefore, even if a small magnetic circuit is intended to be formed, there is a limit to the increase of the efficiency of the head. Moreover, even if a desired head can be available with low yields, there is a problem in that the recording/reproducing efficiency at a shorter wavelength is greatly lowered so that it is not possible to record/reproduce at a high density.